I. Field of the Invention PA1 II. Discussion of the Related Art
This invention relates generally to a fluid forcing pump, and more particularly relates to a fluid forcing pump operable at high pressures. The fluid forcing pump of the present invention includes a housing having a cavity formed therein, wherein the cavity is adapted for receiving a cylindrical rubber impeller assembly of the present invention. The longitudinal axis of the cylindrical rubber impeller assembly and the longitudinal axis of the cavity are offset or eccentric, such that as the cylindrical impeller assembly rotates within the cavity, fluids are displaced through a fluid outlet.
Various conventional rubber impeller pumps have been devised having the ability to pump fluids without a pulsating affect. These conventional rubber impeller pumps typically operate at low pressures and may suffer from high amounts of internal slip, particularly under relatively modest output pressures. The conventional rubber pump rotates a rubber impeller within a cylindrical cavity of a housing, wherein the rotation axis of the impeller is offset from the longitudinal axis of the cylindrical housing (commonly referred to as eccentricity). When the impeller rotates within the cavity of the housing, during a portion of the rotation, the blades are deformed due to the offset or eccentricity between the rotation axis and the housing axis. The blades are typically sized such that blade tips contact the internal wall through the entire revolution of the impeller. Although the blades contact the housing wall, the blades in an eccentric system may deform away from the housing wall allowing fluids to pass between the blades and the housing wall. In order to maintain contact between the conventional blade and the housing wall, the impeller is typically constructed having an outer diameter greater the diameter of the housing bore plus the length of offset. Additionally, the conventional blades may be lengthened to provide an additional "squeeze" by the blades against the housing wall. The pressure limitations of the conventional impeller is limited to the mechanical properties of the material used to construct the impeller. Once the force of the fluid pressure exceeds the mechanical properties of the blade of the conventional impeller, then the blades will disengage from the housing wall, thereby allowing high rates of internal slippage to occur.
The required flexibility of the blades further limits the suitable materials used to manufacture the flexible impeller. The blades of the conventional impeller must be manufactured from a material having resilient properties which allow repetitious bending of the blades of the impeller. Thus, the material selection for the manufacture of a conventional impeller having resilient blades is almost exclusively restricted to elastomers such as neoprene, Buna-N and EPDM. Impellers manufactured from these materials are typically limited to low pressure fluid transfer and circulation applications.
Exemplary of such rubber impeller pumps are those described by E.C. Rumsey in U.S. Pat. No. 2,455,194, Takahashi in U.S. Pat. No. 3,832,105, and McCormick in U.S. Pat. No. 4,940,402. Both Rumsey and McCormick describe rubber impellers having weights secured to the end of each blade. In this manner, the weight is intended to keep the end of the blade in contact with the housing wall as pressure against the blades increases. As the rotation speed of the impeller increases, fluid tends to pass between the impeller and the housing wall limiting the effective speed and maximum operating pressure of the pump. Hence, there is a need for a pump and impeller assembly that may effectively operate at increased rotational speeds and pressure.
Rumsey also describes a slot formed in a central bore of the impeller and a mating rib formed on the shaft of the pump. The impeller is placed on the shaft such that the rib on the pump shaft fits into the slot formed in the central bore of the impeller. Although this "keying" arrangement is intended to reduce the amount the impeller slips on the shaft as the shaft rotates, as the revolutions per minute of the shaft and pressure within the housing increase, the slot may tend to slip over the rib and the impeller may rotate on the shaft. Thus, the effectiveness of this keying arrangement may be dependent upon the speed at which the impeller is rotated and the rigidity of the material used to manufacture the impeller.
Takahashi describes a device that apparently includes a flexible impeller sandwiched between two plates. The impeller is attached to the shaft of the pump, wherein the rotation axis of the impeller is aligned with the rotation axis of the pump shaft. The rotation axis of the pump shaft is offset from the longitudinal axis of the bore formed in the housing. The plates are shown either rotating on a bearing surface or are suspended within the housing such that a portion of the plates bore contacts the pump shaft. The inner surface of the bore on which each plate rotates is subjected to wear and the speed and pressure at which the pump operates may be limited. The blade tips of the impeller slip within slots formed in the plates, such that the plates do not rotate simultaneously with the impellers. Slippage of the blade tips within the slots further limits the pressures at which the Takahashi pump is operable. Hence, there is a need for a rubber impeller pump operable at high speeds and pressures. The present invention addresses these and other needs.